Tom Horne wrote:
On Apr 8, 2:16 pm, Jim Lux wrote:
Tom Horne wrote:
I am interested in having a rapid set up multi-band vertical for Field
Day and EMCOMM. If I use the Hy-Gain sixty four foot (64') push up
mast as the radiator and an ICOM AH-4 as the automatic antenna tuner
is this likely to be an effective approach to having a rapid set up
multi band vertical?
Yes..
You don't need that much height, though.. the loss in radiation
effectiveness going from 1/4 wavelength (20m long) to 1/8 wavelength
(10m) isn't all that big a deal. It's when you get down to the 1/20th
wavelength and the feedpoint Z gets very wild that you have problems
with loss in the matching network.

Will I need radials? Should they be elevated or

can they lie on the ground?
Yes.. you do need radials. Laying on the ground is just fine. Get some
very flexible stranded insulated wire (the kind with lots of fine
strands is better.) and figure a way to rapidly throw it out and store
without tangling. I've thought about spring return reels.

3 or 4 makes a huge difference over 1 or 2. after that, it's a bit of
diminishing returns.. You'd be better off just doing what the people who
do this for a living (rapid deploy HF comms) do.. jack up the Tx power.

BTW, a better approach than a vertical might be a inverted V dipole from
the top of your 60 foot pole. MUCH better radiation effectiveness
because of H polarization..

Since the total length of the radiator is

less than a 1/4 wave on eighty meters at say 3.6 MHz will that make
the antenna ineffective on eighty meters?
Nope.. it's the loss in the tuning network that's the thing to worry
about.. you could make a lumped matching network to feed with your
autotuner if you're worried..



Second question would four of those sixty four foot masts make an
effective forty meter four square. Yes I realize that it would cost
eight hundred dollars for the masts alone before the cost of
controller, remote, phasing coax, and control cable. Once again would
radials be required for forty meters.
Radials are (almost) always required for verticals. even if you don't
install them, your feedline shield will act as a radial with
unpredictable and usually undesirable effects.

Running a 4 square with autotuners at each element is VERY difficult (if
not impossible).. the tuner changes the phase shift, and the interaction
from the other antennas will screw up the auto adjustment algorithm.



I've only been back in radio for a few years after very long gap so
I'm starting over and finding the learning curve a little steeper than
I remember.
--
Tom Horne, W3TDH

Jim
I had no intention of running a four square with four auto tuners.
Perhaps I should have put that inquiry into a separate posting for the
sake of clarity. We built a four square for field day two years ago.
Because the masts that we had then were only thirty feet high a kind
of capacitance hat was built into the guy lines. We had very good
performance from that four square until a severe thunderstorm
destroyed it. I was wondering if having sixty four foot masts would
allow us to adjust the height to resonance on forty meters so that the
four masts themselves could serve as the elements of the four square.
Since a half wave at 7150 kHz is nearly sixty seven feet I would have
to add three feet worth of additional tubing in order to get a
resonant half wave antenna. I had thought that half wave verticals
did not require a counterpoise was I misinformed? If a counterpoise
is needed it wouldn't be too hard to throw out four radials for each
mast. I was just looking for a quick way to put up a four square and
these aluminum masts seemed like they might fill the bill.

Tom, is this a serious exercise here? This is just way too much trouble
for a 40 meter antenna.

Some antennas like the half wave verticals, don't require radials. But
I see a vacillating back and forth between high performance and well,
these verticals, which really aren't High performance.

As for several 64 foot masts, Why not go to one mast and put up a 40
meter beam beam? Add an Amp, and you will rule the air. Although I
wouldn't do that personally, because I would imagine that the idea of
emergency ops is getting set up and running ASAP.


It could be a matter of temperament I guess. You can get most of your
needed performance out of a simple dipole. But if you want to wring the
last drop of performance, I'd have to think the beam would take less
time to set up and perform better than a 4-square. You don't want to
finish installing and tuning just at the time they send everyone home.

- 73 de Mike N3LI -